1. Field of the Invention
The present invention generally relates to a deflection yoke for use in a cathode ray tube, and in particular, to a deflection yoke with improved deflection sensitivity.
2. Description of the Related Art
Cathode ray tubes (CRTs) are used in display devices to produce images. The basic elements of a CRT are a deflection yoke, one or more electron guns, and a phosphor screen. Color applications generally employ three electron guns, one for each primary colorxe2x80x94red, green, and blue. Electron beams emitted by the electron guns are deflected by a deflection yoke. Typically, the deflection yoke consists of two pairs of coils in a CRT. One pair deflects the electron beam primarily in the horizontal direction and is called the horizontal coil. The other pair deflects the beam primarily in the vertical direction and is called the vertical coil.
FIG. 1 depicts a CRT 100 which is cylindrically symmetric. The CRT 100 includes a neck region 102, a funnel region 104 and a phosphor screen 106. FIG. 2 depicts a cross-section of a conventional deflection yoke 200 that has a separator 202 located between a vertical coil 204 and a horizontal coil 206. Also included in the deflection yoke 200 is a ferrite core 210 that serves to enhance magnetic fields 212 produced by the coils 204, 206.
One disadvantage associated with the conventional deflection yoke 200 is that the horizontal coil 206 is positioned a defined distance (D1) away from the ferrite core 210 and therefore the amount of benefit the horizontal coil 206 receives from the ferrite core 210 is reduced. Specifically, the horizontal coil 206 is separated from the core 210 by the vertical coil 204 and the separator 202. The separator 202 is usually a funnel-shaped plastic structure that serves to isolate the horizontal coil 206 in the deflection yoke from the vertical coil 204.
Because the phosphor screen of a CRT is usually rectangular in shape, an electron beam from an electron gun going through the area 208 will never hit the phosphor screen, resulting in a poorer deflection sensitivity. One prior art solution solves this problem by introducing a rectangular deflection yoke 300, as shown in FIG. 3. The funnel region 104 of the CRT is still cylindrical but the rectangular deflection yoke 300 sits in the neck area 102 of the CRT. Since an unnecessary region 208 in FIG. 2 is eliminated, the deflection sensitivity (deflection per unit current) is increased and the amount of stored energy (E=xc2xd LI2) in the yoke 300 is decreased, where L is the horizontal coil inductance and I is the peak horizontal current.
It is well known in the art that when the stored energy of a deflection yoke is lowered or deflection sensitivity is improved, the cost of the deflection circuit is decreased. Also, certain countries (e.g., Japan) will soon require all televisions to satisfy overall power consumption limitations/requirements. It is also known in the art that by increasing the deflection sensitivity, the amount of power consumption required by the deflection circuit may be reduced. Thus, there is market pressure to find methods of lowering the stored energy and improving deflection sensitivity in a deflection yoke.
In accordance with one embodiment of the present invention, a deflection yoke is provided for use in a cathode ray tube, which has an improved deflection sensitivity. The deflection yoke includes a ferrite core, a vertical coil to generate a vertically defecting magnetic field and a horizontal coil to generated a horizontally deflecting magnetic field. The core has a funnel-shaped body with an opening therethrough defining an inner surface. The horizontal coil includes a pair of saddle-type coils positioned in the core such that at least a portion of the horizontal coil is in contact with the inner surface of the core.
In one embodiment, channels are provided in the core that extend along the entire core length. The channels are configured to receive the vertical coil and is wider towards a large diameter end of the core and narrower towards a small diameter end of the core. By placing a vertical coil within each of the channels, the vertical coils can be supported by the core without significantly affecting the positioning relationship of the horizontal coil with respect the inner surface of the core. In one implementation, more than one half of the outer surface area of the horizontal coil is in contact with the inner surface of the core.